This invention relates to membranes adapted for the waterproofing and sealing of substrate structures, particularly in roofing applications. More particularly, this invention relates to waterproofing membrane laminates adapted to have improved dimensional stability and to exhibit minimal adverse physical change in their laminar structure under the conditions of high temperature normally encountered in a roof top environment.
Flexible sheet-like laminates of support films and self-adhesive bituminous waterproofing layers pre-formed in the factory have been successfully employed in roofing applications as substitutes for the more conventional waterproofing membranes which are constructed at the job site by plying together one or more layers of bitumen-saturated paper or felt and bituminous adhesives. The pre-formed, self-adhesive laminate-membranes offer many advantages including factory controlled preparation, avoidance of heating equipment and handling of hot materials at the job site, as well as many performance advantages.
Flexible pre-formed laminates of the aforementioned type and their use to form waterproofing layers in various kinds of building structures are described for example in U.S. Pat. Nos. 3,741,856; 3,853,682; and 3,900,102 to John Hurst. Such patents describe in particular the preparation of flexible laminates containing a support material, for example a layer of a polymeric or metallic film, and a layer of self-adhesive or pressure-sensitive adhesive, bitumen-elastomer waterproofing composition. As discussed in particular in U.S. Pat. No. 3,900,102, such laminates may ideally be constructed in the plant in the form of a roll with a protective sheet, for example siliconized paper applied against the self-adhesive bituminous waterproofing layer, transported to the job site, and thereafter applied to a substrate adhesive side down, each successive laminate strip being made to overlap the edge of the previously applied strip of laminate to insure a continuous waterproofing seal.
U.S. Pat. No. 4,396,665 of Paul E. Rowe relates to an improved laminate which employs a thin layer of metal film or foil positioned between and adhered to a polymeric film and a layer of a waterproofing pressure-sensitive adhesive or self-adhesive bituminous composition. These laminates may be viewed as comprising a "composite" support system, consisting of the polymer film-metal film laminate which carries or supports the adhesive layer. Oriented polymer films, such as those of Canadian Pat. No. 1,008,738, are the preferred polymer films for use in these laminates. Such oriented films, which can be biaxially oriented or oriented and cross-laminated films, exhibit reduced wrinkling following adhesion to a substrate and subsequent exposure to heat, for example, exposure to the sun. The thin metal layer provides increased fire protection; prevents oils in the bituminous composition from contacting the polymer film, with a resultant increase in the physical and chemical stability of the film; and, since it is rigidly bonded to the film and has a substantially lower coefficient of thermal expansion, provides a realtively high level of dimensional stability to the laminate under high temperature conditions. In addition, the relative coefficient of thermal expansion of the film and foil are such that, at elevated temperatures, the edges of the laminate tend to curl downward so as to provide a "self-sealing" effect in overlapping (joint) areas of adjacent, overlapping laminates.
Although the laminates of the aforementioned application, and more specifically the composite support system thereof, provide certain advantages, they can be further improved or optimized for roofing applications. For example, when the laminates are subjected to the relatively high surface temperatures of the black roof environment, e.g., above 160.degree. F., the oriented polymer film has been found to undergo cracking leading to membrane degradation. This adversely affects the appearance of the membrane, largely eliminates the protection originally afforded the underlying foil and bituminous adhesive by the polymer film, and increases the possibility of leakage, particularly at overlap joints between adjacent membranes. In addition, when subjected to the relatively high temperature conditions of 130.degree. F. or greater, the laminates display a marked propensity to reverse any tendency for downward curl and to instead curl upward at their edges, again increasing the possibility of leakage at overlap joints. Thus, it has been desired to provide improved waterproofing laminates which have the aforedescribed composite support system and incorporate the advantages thereof but which do not exhibit cracking or peeling of the polymer film or upward edge curling upon exposure to high temperatures.